Apparatus and method for controlling freezing of ingots



March 30, 1937. E. J. KAILJFFMAN 2,075,039

APPARATUS AND METHOD FOR CONTROLLING FREEZING OF INGOTS Filed Nov. 16-, 1934 4 Sheets-Sheet 1 I v i d INVENTOR. a idmmdffazflzrmia M ATTORNEYS March 1937- E. J. KAUFFMAN 2,075,039

APPARATUS AND METHOD FOR CONTROLLING FREEZING OF INGOTS Filed NOV. 16, 1934 4 Sheets-Sheet 2 A r 'IIIIIIIIIIIIM [dz/221725 .ffizfliizaiz 5 BY @M /KQZ- ATTORNEYS March 30, 1937. E. J. KAUFFMAN 2,075,039

APPARATUS AND METHOD FOR CONTROLLING FREEZING OF INGOTS Filed Nov. 16, 1954 4 Sheets-Sheet 3 I 77 ////M/4/ 16 r In a - INVENTOR. I

ATTORNEYS March 30, 1937. E. J. KAUFFMA N 2,075,039

APPARATUS AND METHOD FOR CONTROLLING FREEZING OF INGOTS Filed Nov. 16, 1934 4 Sheets-Sheet 4 v f-M ATTORNEYS 1 WM NwIII T j 1 d lll'ul' m, A ,1 3 v. \JWMQIAIIIIIIIIA w a y W 3 ell/ Patented Mar. 30, 1937 UNITED STATES APPARATUS AND METHOD FOR CONTROL- LING FREEZING OF INGOTS Edmund J; Kaulfman, Girard, Ohio, assignor to Valley Mould & Iron Corporation, Hubbard, Ohio, a corporation of New York Application November 16, 1934, Serial No. 753,297 10 Claims. (01. ea-zoo) The present invention relates primarily to metallurgy and more specifically to an apparatus and method of controlling the freezing of ingots. It is further specifically related to the controlling of the freezing of steel ingots in molds equipped with hot tops.

Ingots formed in molds equipped with hot tops, and more especially molds of the big-end-up type, are with few exceptions, made from fully de-oxydized or killed steel. Such ingots are subject to internal cracks or ruptures extending longitudinally of the ingot and are known to those skilled in the art as internal columnar dendritic ruptures", or more colloquially known as internal 1.; point cracks. The lower carbon nickel steels some of the higher carbon plain steels, and in general, steels used for gears and high grade forgings are particularly subject to this very serious and dangerous defect.

-30 The defects specified are brought about by per-.

mitting the ingot to stand in the mold until it is substantially frozen. During the freezing of the steel, the metal of the ingot shrinks as it solidifies, withdrawing the surface of the ingot from the matrix side walls of the molds. In substantially all cases, the frozen ingot tipsto one side, thereby leaving one side of the ingot in contact with the mold and the other side of the ingot spaced apart from the matrix walls of the mold. This results 30in an uneven cooling of the ingot which develops these serious cracks, usually comprising hidden flaws, which result in very serious and dangerous weaknesses in the finished products. Attempts are made to avoid the flaws specified by removing the ingot from the mold before it is completely solidified. In order to do this, it becomes necessary to removethe hottop. As. soon as the hot top is removed, the hot metal in the upper end of the ingot quickly freezes and the result is serious 40 piping and porosity within the interior of the ingot as well as non-uniform freezing due to air drafts and other factors. It, therefore,.is apparent that the metallurgist in attempting to cure one evil develops another which likewise produces serious defects.

The present invention overcomes the difliculties above specified and obviates the defects in the ingot by the method of longitudinally sliding the ingot within the mold, therebyobtaining addition- 50 al air space between the ingot and the mold due to the taper of the matrix of the mold, maintaining the ingot centrally located within the mold to provide the air space between the ingot and themold substantially uniform, then retaining theingot within the mold until the ingot is substantially frozen, and with a hot top in position on the ingot during the period the ingot remains within the mold'.

The preferred apparatus comprising one em- 60 bodiment of the present invention is mechanism such as a thrust plug to lift the ingot, and mechanism to guide and hold the ingot centrally located within the mold. The guide, which preferably is for the upper end of the ingot, may cooperate with the hot top or may cooperate directly with the ingot.

' The disclosure herewith is illustrative of the present invention, and, therefore, is not to be considered in the limiting sense since it is realized that the present invention may be carried out with, and embodied in, structures other than those specifically disclosed herewith.

Fig. 1 is a cross-sectional'view on line AA of Fig. 5, illustrating the relation of the mold and the metal within the mold shortly after the pouring is completed.

Fig. 2 is a section on line AA of Fig. 5 showing the relation of the metal within the mold and the mold during a later period in the stage of freezing.

Fig'. 3 is a section on line A-A of Fig. 5 illustrating a still further stage in the freezing of the tially frozen and illustrating the formation ofinternal columnar dendritic ruptures at the comers of the ingot adjacent sides of the ingot which have been in contact with the mold.

Fig. 5 is a vertical cross-section through the mold and ingot with the cross-section being taken through the ingot on line BB of Fig. 4. Fig. 6 is a section through a big-end-up ingot to which applicants invention has been applied. This section is on the same plane as section A --A and corresponds to the stage of freezing of th defective ingot illustrated in Fig. 3.

Fig. 7 illustrates a vertical cross-section through a mold showing the initial stage of freezing of the metal in the mold with the set-up including a refractory type hot top telesooped into'the upper end of the mold. 4

Fig. 8 illustrates applicantsmethod of control as applied to the ingot illustrated in the mold in Fig. 7.

Fig. 9 is a plan view of the construction illustrated in Fig. 8. i

Fig. 10, is a vertical section through the upper end of a big-end-up mold equipped with apparatus embodying the present invention comprising guide pins for guiding the vertical movement of the hot top.

end of the ingot, which sleeve is mounted on the mold. I Fig. 13 illustrates a' cross-section of a modifi- 25 cracks.

cation of the embodiment illustrated in Fig. 12 comprising a hot top having a supporting shell guided by centering guide arms mounted on the mold.

5 Fig. 14 illustrates a vertical cross-section of an ingot mold and ingot with the ingot mold provided with an inward taper adjacent the upper end thereof to guide and center the raised ingot within the mold.

Fig. illustrates a vertical cross-section of the upper endof an ingot mold with a hot top construction mounted within a shield of refractory material supported in a shell provided with guides cooperating with the shell of the hot top.

15 It is to be understood that the mold constructions illustrated in Figs. 10, 11, 12, 13 and 15 have the same lower constructions as are illustrated in Figs. 7, 8, and 14 and that the ingot has been raised in the Figs. 10, 11, 12, 13, and 15.

Fig. 1 illustrates a cross-section on line A--A of Fig. 5 and shows an ingot mold I having an eight sided fluted matrix. This type of contour is frequently used in the art to produce steel ingots that are most subject to internal point The molten metal which will form the ingot 2 within the mold is illustrated as beginning to form a skin 4 of dendritic columnar crystals with the skin 4 in contact with the walls of the matrix. At the stage of the freezing illustrated in Fig. 1, the skin 4 on the ingot is very thin and hot, and, therefore, is elastic and the metallo-static pressure of the molten interior metal forces this initial skin firmly against the- The crystals have pulled away from the recesses 6 of the mold leaving the side walls I of the ingot in contact with the side walls 8 of the mold. This pulling away action at the corners may be due to several causes, one of which*may be the tendency. of the shrinking ingot to cause the circumference thereof to approach a more nearly circular form. As soon as the ingot breaks contact with the recesses 6 of the matrix of the mold, the direct conduction of heat at these zones is interrupted, thus causing the salients or corners on the ingot to increase in temperature due to, heat from the molten interior, while the zones 1, which are retained in contact with the mold wall, are being rapidly cooled as the heat of these side zones is absorbed by the mold. This interrupts. the growth of the acicular dendritic crystals at the corners while this type of crystals continues to grow on the sides of the ingot in contact with the mold.

Fig. 3 illustrates a further stage in the freezing of theingot at which the circumference of the mold and an air space extends around four of the sides of the eight sided ingot. As the ingot continues to freeze, the result 'is that the growth of the acicular dendritic crystals on the four side 7 walls I greatly predominate over the growth of these crystals on the other four side walls 9. Consequently, the freezing of the ingot and the crystallization thereof is unbalanced. This causes the formation of the internal point cracks l I illustrated in Figs. 4 and 5. These cracks ordinarily do not come entirely to the surface of the ingot although in exaggerated cases, that may happen. One reason for these internal cracks occurring at the corners and beneath the initial skin appears to be that the outer skin is usually of suflicient strength to resist shrinkage forces without cracking while the metal between the outer skin and the liquid core is weak. Since the shrinkage occurs most rapidly on the side faces, because they are in contact with the mold while the corners are out of contact, the metal of'the ingot side walls inside the initial skin shrinks, and as it shrinks the crystals tend to swing-like stalks of wheat to-' ward the middle of the side walls. This tendency becomes so great and the hot metal inside the initial skin is of such low strength that voids occur where opposing shrinkage forces meet, thereby separating the crystals being pulled in one direction from adjacent crystals being pulled in the other direction. This occurs adjacent the corners which are not in direct contact with the mold. The result is longitudinal voids in the ingot comprising internal columnar dendritic ruptures such as are illustrated in Figs. 4 and 5.

It has been found by experiment that where the length of the acicular dendritic crystals in the middle of the side walls greatly exceeds the length of the dendritic crystals in the salients or corners, internal columnar dendritic ruptures are likely to appear. Referring to Fig. 3 and assuming the length of the dendritic crystals in the side wall out of the contact with the mold be represented by the character T and that the dendritic crystals of the adjacent corner be represented by the character K. If the ratio of T divided by K is not greater than the empirical number 2.25, the ruptures do not occur. On the opposite sides of the ingot illustrated in Fig. 3,-where the ratio of T| divided by Kl, exceeds 2.25, ruptures do occur;

Where the ingot is held with its axis coincident with the axis of the mold so that the ingot cannot tip sidewise in the mold, then a condition is produced which is illustrated in Fig. 6, wherein a continuous air space, entirely around and substantially uniform, is provided betweerf the matrix side a walls and the ingot.

Fig. 7 illustrates the initial freezing of an ingot' in'a big-end-up mold shortly after complete pouring and wherein the initial skin has just begun to shrink. At this stage of freezing, the lower portion and the upper portion of the ingot have substantially receded from the mold walls, whereas the middle portion indicated at l2--|4 in Fig. 7 is still substantially in contact. In other words, the ingot is somewhat barrel-shaped. This is due to the fact that the lower portion being poured first has had a longer time to cool and acquired strength, and the upper pprtion being under less metallo-static head already has suflicient strength to resist internal forces and to recede slightly from the mold walls. The middle zone has not sufficient strength to resist thase internal forces and remains longer in contact withthe matrix walls than other portions of the ingot. Very'shortly in the mold without rupture of the mold skin.

Fig. 8 illustrates the ingot 2 as being slid longitudinally in the mold l by means of a bottom plug l5 which contacts with the stool IS. The upper portion of this plug I5 is tapering while the lower part is cylindrical to be guided by the opening in the mold. This stool I6 is provided with an opening I! to receive the plug H) at the time when the metal is poured as shown in Fig. 7. After the initial ingot skin has reached the stage sufficient to support the molten metal within the ingot, the mold is raised by lugs commonly provided on ingot molds, shifted slightly on the stool I6 and set down with the end of the plug I 5 contacting with the surface of the stool so that the weight of the mold l causes it to drop away from the ingot. As soon as this occurs, spacing plates i8 may be inserted between the mold and the ingot, as illustrated in Figs, 8 and 9, to hold the ingot centrally positioned within the mold and with a substantially uniform air space l9 around the ingot. In the construction illustrated in Fig. 8, the upper end of the ingot is unprotected. While the present invention may be carried out in this manner, it is preferable that the upper end of the ingot be protected against air cooling.

Fig. 9 is a plan view of the structure illustrated in Fig. 8, and shows a substantially rectangular contour mold provided with lifting lugs 20 common in the art. It is to be understood that the present invention is not confined to any particular cross-section contour of the matrix'of a mold. The contour chosen in Figs. 1 to 6 more fully illustrates the invention, as a contour in common use and one wherein the difliculties here overcome most frequently occur. These same difficulties, however, occur with any mold in which the ingot tips sidewise to contact with the mold walls on one side only and thereby be unequally movable through bearings 25 in the top of the mold. A shield may be provided around the lower portion of the hot top and is of sufflcient length to protect the upper end of the ingot against air cooling when the ingot has been pushed upwardly to extend slightly from the mold. The pins 24 perform the double function of centering the hot top shell 2| over the mold and also-of providing guides which hold the upper end of the ingot centrally located relative to the mold matrix when the ingot has been moved longitudinally in the mold.

Fig. 11 illustrates a modification of a construction shown in Fig. and wherein a guide shield is provided to center the hot top on the mold and to guide the hot top when the ingot is lifted in the mold; Either member, 1 e., the mold or hot top, may carry the shield 26 so long as it is held in place to perform the function of guiding the relative movement of these parts to maintain {he ingot centrally located when thedngot is ifted.

Fig. 12 illustrates asection through the upper end of the mold and hot top wherein the hot top is similar to that illustrated in Fig. '7 and is guided in its upward movement by a flange comprising a guide shield 28 for the ingot when it is lifted. 'I'his'flange guide member 28 is preferably carried by the mold I and may be secured therekey pins 21.

to by key pins 21 passing through the edge of the flange 28 and lugs 29 provided on the mold I.

Fig. 13 illustrates a refractory lined hot top having a metallic shell provided with a cylindrical portion 30 adapted to cooperate with guide fingers 3i secured to the upper end of the mold by the Fig. 14 illustrates a mold set-up in which the major portion of the matrix 32 has an upward and outward taper, whereas the matrix from the point 34 to the mouth of the mold is provided with an inward taper 35' of such amount as to contact with the upper end of the ingot when it is raised to position the same centrally within the mold I. In this construction, the hot top 36 telescopes within the mold so that the bottom of the hot top during pouring is located substantially at the point 34 or slightly below in the matrix of the mold. I

Fig. illustrates a further modification of the present invention in which a flange 36 is secured to the mold body by key pins 21 andthe interior face of the flange is lined with refractory nateriag 31 to act as a heat insulator for the upper *end of the ingot 2 when the same is lifted to provide the uniform air space l9 around the ingot. This flange is provided with guide lugs 38 which cooperate with the cylindrical portion 30 on the hot top to guide the same.

It is to be understood that if Figs. 10, 11, 12, 13, and 15 were completed, the lower portions of the figures would be identical with the full construe-- including the sink head portion is 10,050 pounds and the weight of the ingot plus the sink head is 12,100 pounds. Assume that the steel is to be 30% carbon or less with 3.50% nickel, which is a steel that is, very sensitive to the development of these internal corner cracks. For this size mold, the rate of pouring of metal at normal pouring temperatures is not to exceed the rate of one gross ton per minute. After the pour is completed, the ingot should remain quietly in the mold with the hot top thereon for approximately one and three quarter hours. At the expiration, of this time, the mold is lifted by lift rig 39 (Fig. 7) attached to a suitable overhead crane. The lift rig 39 engages the lugs 20 provided for this purpose and the mold when lifted is moved sufliciently to cause the centering and ejecting plug ii to engage the top surface of the stool l6 when the mold is lowered, thereby causing the moldsto drop away from the ingot or in other words, causing a relative longitudinal movement between the ingot and the mold. Preferably, the amount of the relative movement is substantially eight inches. The preferred taper of the mold is such as will provide substantially a one quarter inch space between the surface of theingot and the matrix side walls of the mold for the movement specified. The air shield provided prevents air cooling the upper end of the ingot and the lifting of the ingot relatively to the mold has caused the upper end thereof to snugly fit within the not top which has been accurately guided and held in its final position to substantially center the ingot in the manner specified. The ingot and mold are preferably retained in their telescoped relation for three or four hours, after which the ingot may be stripped from the mold in the usual manner and thereafter treated in accordance with the specific procedure of the mill utilizing the present inventions by removing the ingot to a suitable pit or to a re heating furnace for direct forging or rolling as the case may be.

It is to be understood that for different sized molds and ingots the pouring speed and the time the ingot remains in the mold are to be varied according to the teaching of the art well known to those skilled in the art.

An important feature of the invention is the maintenance of the uniform air space around the ingot during the final stages of freezing of the ingot, and preferably until the dendritic crystals have substantially ceased to form in the ingot.

What I claim is:

1. In a device of.the class described, a big-endup ingot mold, a hot top movably mounted on said mold, the hot top being of rigid construction which becomes attached to the ingot, means to cause a relative longitudinal bodily movement between said mold and a partially frozen ingot therein, and means to positively guide said rigid hot top during said movement to retain the axis of said ingot substantially coincident with the axis of the matrix of said mold when said movement has occurred.

2. Apparatus for casting ingots and soaking them in the mold duringthe later stages of solidification, comprising: a big-end-up ingot mold; a hot top mounted movably on said mold to permit the hot top to remain in place on the ingot during them in the mold during the later stages of solidification, comprising; a big-end-up ingot mold; a hot top mounted movably on said mold to permit the hot top to remain in place onthe ingot during partial stripping of an ingot cast in said mold;

means to partially strip the ingot, sufliciently to establish a heat insulating air space between the ingot and the mold, said construction maintain-,

ing said air space closed against the circulation therethrough of substantial currents of cooling air; and means to ,hold the ingot coaxialwith the mold upon completion of said partial stripping.

4. Apparatus for casting ingots and soaking them in the mold during the later stages of solidification, comprising: a big-end-up ingot mold;

a hot top mounted on said mold; means to partially strip an ingot cast'in said mold, sufficiently to establish a heat insulating air space between the ingot and the mold, said construction maintaining said air space closed against the circulation therethrough of substantial currents of cooling air'; and a telescopic connection between said hot top and said mold, said connection permitting the hot top to remain on the ingot during said partial stripping and. then maintaining the ingot coaxial with the mold.

.5. Apparatus for casting ingots and soaking them in the mold during'thelater stages of solidification, comprising: a big-end-up ingot mold;

means to partially strip an ingot cast in said mold, sufficiently to establish a heat insulating air space between the ingot and the mold, said construction maintaining said air space closed against the circulation therethrough of substantial currents of cooling air; and means to maintain the ingot coaxial with the mold after said partial stripping has been effected.

6. Apparatus for casting ingots and soaking them in the mold during the later stages of solidification, comprising: a big-end-up ingot mold; a hot top mounted on said mold, free to be separated therefrom in an axial direction; means to partially strip an ingot cast in the mold, sufiiciently to separate the hot top from the mold and establish a heat insulating air space between the ingot and. the mold, said construction maintaining said air space closed against the circulation therethrough of substantial currents of cooling air; and means to hold the ingot coaxial with the mold upon completion of said partial stripping and also shield the ingot from cooling currents in the zone between the mold and the hot top.

'7. The method of controlling the freezing of a steel ingot after it has been poured in a tapered ingot mold, which comprises: partially stripping the ingot, sufliciently to establish a through said space.

8. The method of controlling the freezing of a steel ingot after it has been poured in a tapered ingot mold, which comprises: partially stripping the ingot when the sides of the ingot have frozen to a self-supporting thickness, the partial stripping being sufficient to establish a heat insulating air space between the ingot and the mold; maintaining said air space substantially uniform about the periphery of the ingot, heat insulating the upper end of the ingot, and preventing substantial circulation of cooling air through said space.

9. The method of controlling the freezing of a steel ingot after it has been poured in a tapered ingot mold, which comprises: partially stripping the ingot, sufiiciently to establish a heat insulating'air space between the ingot and the mold while leaving the major portion of the ingot inside of the mold; preventing substantial circulation of cooling air through said space; heat insulating the upper end of the ingot; and main ing the projecting portion of the ingot from cooling currents of air; and maintaining the ingot coaxial with the mold in said partially stripped position until dendritic crystals have substantially ceased to form in the ingot.

EDMUND J. KAUFF'MAN. 

